Previously, there is known an acceleration device that controls an acceleration state of a vehicle according to the amount of depression of a pedal by a driver of the vehicle. The acceleration device includes: the pedal, which is depressible by the driver; a shaft, which is rotatable according to a rotational angle of a pedal arm connected to the pedal; and a housing, which rotatably supports the shaft and is to be fixed to a body of the vehicle. A boss portion, which is connected to the pedal arm and is rotatable integrally with the shaft, is provided to an outer wall of the shaft located at a radially outer side of the shaft.
The boss portion is rotatably received in a communication passage, which communicates between an inside of the housing and an outside, and a gap is formed between an outer wall of the boss portion, which is located at a radially outer side of the boss portion, and an inner wall of the housing, which forms the communication passage. Thus, there is a possibility of that foreign objects, which are contained in the air passing through the gap, enter the inside of the housing. The foreign objects, which enter the inside of the housing, may have negative influences on, for example, rotation of the shaft. In view of the above disadvantage, for example, the patent literature 1 discloses an acceleration device, which has projections at both of the radially outer wall of the boss portion, which is located at the radially outer side of the boss portion, and the inner wall of the housing, which forms the communication passage.
However, in the acceleration device of the patent literature 1, since the projections are formed at both of the radially outer wall of the boss portion, which is located at the radially outer side of the boss portion, and the inner wall of the housing, which forms the communication passage, the foreign objects, which have entered into the inside of the housing, cannot be easily discharged to the outside through the gap. Therefore, the foreign objects tend to be accumulated in the inside of the housing, and thereby there is a possibility of causing negative influences on, for example, the rotation of the shaft.